Subscription television and cable television are becoming increasingly popular. As a result of such increasing popularity, however, unauthorized use of the programming from these sources is becoming a very significant problem. Many systems have been proposed to scramble the television signals in various fashions to deter unauthorized utilization of the programming. Many of the systems currently employed either are overly complicated electrically such that the circuitry to reconstruct the signal is expensive, or are not sophisticated enough to deter unauthorized utilization of the television signals.
Prior art systems currently in use usually employ one of several standard techniques. One technique is to invert all of the video program information, along with the horizontal sync and blanking information present in a composite video signal. The disadvantage of this approach is that, for those skilled in video technology, such inversion is easy to detect and the signal can be easily reinverted, especially with the presence of the horizontal sync and blanking information.
Another technique employed is to transmit all of the horizontal sync and blanking pulses, but to randomly invert the video program information. This particular approach presents difficulties in accurately reconstructing the video signal and often results in a flickering picture.
Furthermore, in most subscription television or cable systems, data must often be transmitted to the subscriber's decoder to identify, for example, the types of programmaing to which the subscriber has subscribed and is thus entitled to view. Several techniques have been used to transmit such data. With one system, data is transmitted over unused horizontal scanning lines during the vertical blanking interval of the broadcast signal. As only a limited number of such lines are available, data is transmitted at a very high rate, requiring expensive high-speed digital devices in the decoder to accurately store and process this data.
Other techniques employ additional FM or audio subcarriers to transmit this data, also resulting in complicated transmission networks and additional circuitry in the decoder. These particular techniques are also restricted by available bandwidth, resulting in low-speed transmission.
No prior art system discloses or suggests a system which would allow the following functions to be performed simultaneously and independently: random inversion of the video program information, inversion of the horizontal blanking and sync information, and DC level biasing of the horizontal blanking and sync information. Furthermore, no prior art system discloses or suggests a system which would allow the continual transmission of data in a scrambled composite video signal which would provide a decoder with the necessary information to decode such a signal.
Accordingly, it is the principal object of the present invention to deter unauthorized utilization of a video signal.
Another object of the present invention is to allow the following operations to be performed simultaneously and independently in a composite video signal: random inversion of the video program information, biasing of the horizontal blanking and sync information, and inversion of the horizontal blanking and sync information.
Yet another object of the present invention is to effect high-speed digital data transmission in a scrambled composite video signal.